The apparatus of the present invention is composed of a stroboscope, a color television camera, an IC memory, a color television monitor and the like. The apparatus is principally designed to display, on a color television monitor, a dragonfly mark, deviations in a print, contamination in a print, a dot, etc., as a stationary image, during the operation of a multi-color printing offset printer, so that an operator may monitor them.
Conventional methods for monitoring the dragonfly mark, the deviations in a print, the contamination in a print, the dot, etc. during multi-color printing include a method in which strobe light is synchronously emitted so as to illuminate the printed matter so that the operator may directly monitor its condition using his eyes, and a method in which a polygonal mirror is synchronously rotated towards the printed matter.
However, the former method has the following disadvantages:
(1) An excessive flicker (particularly at a low speed), thus failing to achieve accurate monitoring.
(2) Due to the flicker, the operator becomes severely fatigued.
(3) Unavoidable stray light influences occur because of the nature of the working environment, thereby causing a monitor image which is not completely stationary.
(4) The effective field of vision is excessively narrow.
The latter method has the following disadvantages:
(1) Since the apparatus is mechanical, the apparatus is large in size, and a considerable modification of the printer itself is necessary.
(2) The change in flow size of the printed matter cannot be made simple.
(3) The field of vision is narrow because of the nature of the configuration.
(4) Since there is inherent flicker, there poses a problem with respect to continuous monitoring.
(5) Since the monitoring position is limited, it is difficult to interlock with the operating sections of the printing machine.
(6) The apparatus cannot be moved to other printing machines.